In recent years, more and more products employ solid light sources such as LEDs (Light Emitting Diode) and LDs (Laser Diode) instead of existing mercury lamps, xenon lamps, or the like, as light sources used for presentation or digital cinema projectors. A long-life fixed light source such as an LED does not need conventional replacement of lamps and lights up immediately at power-on, which are advantageous.
One type of such a projector employs a solid light source as an excitation light source. A phosphor or the like is irradiated with light from a solid light source as excitation light, and the phosphor or the like is used to display an image. For example, blue light, and red light and green light generated excited by the blue light as excitation light are used to display a color image.
For example, according to a light source apparatus of Patent Document 1, a phosphor wheel is irradiated with blue laser light as excitation light. The phosphor wheel includes a base and a phosphor layer formed thereon. The phosphor layer is irradiated with the excitation light, and yellow fluorescence is thus generated. The blue light and the yellow light emitted from the phosphor layer are synthesized, and white light is thus emitted (Patent Document 1, paragraphs [0028], [0029], etc.).
According to the disclosure of Patent Document 1, the phosphor wheel generates heat when it is irradiated with laser light. For example, if the phosphor wheel is irradiated with a larger amount of light to increase output of the light source apparatus, then the phosphor wheel generates a larger amount of heat. According to Patent Document 1, a predetermined position of the phosphor wheel is irradiated with excitation light while rotating the phosphor wheel to cool down the phosphor wheel. Further, by using a crystalline member such as crystal and sapphire having a higher thermal conductivity as the base of the phosphor wheel, cooling performance is increased (Patent Document 1, paragraphs [0005], [0006], etc.).    Patent Document 1: Japanese Patent Application Laid-open No. 2012-173593